However, it was demonstrated that type I IFN pathway upregulation was correlated with increased expression of a subset of six ISG (IFI27, IFI44L, IFIT1, ISG15, RSAD2, and SIGLEC1) by quantitative polymerase chain reaction assays with whole blood samples in AGS patients, the so-called interferon signature. This evidence concerns the gene ISG15 and Aicardi-Goutieres syndrome.